Pavlovian inhibitory conditioning and tolerance to pentobarbital-induced hypothermia in rats.

One group of rats (discrimination group) from an S pool of 96 male Sprague-Dawley rats received training in which, on alternate days, 1 conditioned stimulus (CS+) was associated with administration of 30 mg/kg pentobarbital (PBB), and a different CS (CS–) with saline. Controls received either exposure to both CSs but not the drug or to the drug but no CSs or to neither the CSs nor the drug. Subsequently, half the Ss in each group received injections of PBB in the presence of one of the CSs and the remaining half in the presence of the other CS. Results show that the discrimination group injected with PBB in the presence of CS+ displayed the most tolerance, whereas the discrimination group injected with PBB in the presence of CS– displayed the least tolerance. The attenuation of tolerance in the discrimination group injected in the presence of CS– provides evidence of inhibitory Pavlovian conditioning. Additional evidence of inhibitory conditioning was provided by the fact that CS? enhanced the hypothermic effects of PBB in the discrimination group, whereas CS? attenuated these effects. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)